Wireless footswitch and functional electrical stimulation apparatus

ABSTRACT

A shoe insole has a cavity configured to provide an internal pocket open to a face of said insole, conveniently the lower face, the cavity having a length greater than its width and being directed generally along the length of the insole. A segmented structure is slideably insertable into said cavity within it is removably retained, the segments being disposed along the cavity and housing a pressure sensor, sensor state monitoring circuits, a wireless transceiver and a battery, adjacent segments being electrically connected together and hinged together by pairs of laterally spaced connector bars each mechanically connected together by links configured to maintaining the spacing between segments while permitting flexion between adjacent segments under loads encountered during walking.

RELATED APPLICATIONS

This application is a U.S. National Stage Application filed under 35U.S.C. §371 of International Application Serial NumberPCT/GB2012/052612, filed Oct. 22, 2012 and published as WO 2013/061038A3 on May 2, 2013, which claims priority to United Kingdom PatentApplication Serial No. 1118580.8, filed Oct. 27, 2011; whichapplications and publication are incorporated herein by reference intheir entirety.

FIELD OF THE INVENTION

The present invention relates to a wireless footswitch module, to awireless footswitch in which a module as aforesaid fits into an insole,and to a FES system comprising a wireless footswitch and a FES devicefor attachment to the human body for stimulation of one or more musclegroups in response to signals from said stimulator. It also relates tothe use of the stimulator for treating a variety of conditions, inembodiments for treating dropped foot

BACKGROUND TO THE INVENTION

In embodiments, the invention provides apparatus for applying anelectrical stimulus to a person's leg in timed relationship to legmovement during walking in order to achieve a benefit.

For example, a person who has a dropped foot is unable to lift his orher toes clear of the ground during the swing phase of walking. Such aproblem is seen in people who have either a peripheral nerve lesion, asa result of trauma or disease, or an upper motor neuron lesion. It isthe latter that responds to neuromuscular stimulation. Lesions of thelower motor neurons result in destruction of the neural pathway so thatmuscle contraction can be achieved only through direct stimulation ofthe muscle fibers. Functional electrical stimulation may therefore besuitable for the treatment of patients following stroke, multiplesclerosis, spinal cord injury T-12 and above, Parkinson's disease,cerebral palsy, head injury and familial or hereditary spasticparaparesis.

The first reference to functional electrical stimulation (FES) is thework by Liberson et al, “Functional electrotherapy in stimulation of theperoneal nerve synchronized with the swing phase of gait of hemiplegicpatients”, Arch. Phys. Med. Rehabil. 42, 202-205 (1961). At this timeelectrotherapy was commonplace, but functional electrotherapy was a newconcept. Liberson defined it as follows: ‘ . . . to provide the muscleswith electrical stimulation so that at the very time of the stimulationthe muscle contraction has a functional purpose, either in locomotion orin prehension or in other muscle activity. In other words, functionalelectrotherapy is a form of replacement therapy in cases where impulsescoming from the central nervous system are lacking.’

Liberson used a portable stimulator to correct drop foot during walkingA train of pulses of 20-250 μsec duration, frequency 30-100 Hz andmaximum peak current 90 mA was applied through conductive rubberelectrodes. The negative (active) electrode was placed over the commonperoneal nerve below the knee and the large indifferent electrode eitheron the thigh or on the lower leg. The stimulator was worn in the pocketand a heel switch was used to trigger the stimulus during the swingphase of the gait cycle. The switch was worn within the shoe or on thefoot on the affected side so that the electrical circuit was interruptedduring the stance phase, when the weight was on the heel, and allowed toflow when the heel was lifted during the swing phase. Liberson wasenthusiastic about the results, reporting that all the subjectsexperienced considerable improvement in gait. Despite improvements inthe apparatus used, the basic idea of FES has remained unchanged.Sixteen papers on the topic published in the period 1960-1977 have beenreviewed by J. H. Burridge et al, Reviews in Clinical Gerontology, 8,155-161 (1998).

U.S. Pat. No. 6,507,757 (Swain, the contents of which are incorporatedherein by reference) is concerned with improving the reliability of thefoot switch. In one aspect it discloses a functional electricalstimulator for attachment to a leg comprising: first and secondelectrodes for attachment to the leg to apply an electrical stimulus; afoot switch for sensing foot rise or foot strike, said foot switchcomprising a force-sensitive resistor; a circuit responsive to said footswitch for generating stimulation pulses; and means forming part of saidcircuit for responding to changes in the resistance characteristics ofsaid foot switch by adjusting a corresponding response threshold of saidcircuit.

Various proposals have been made for providing a wireless link between aFES stimulation module and a footswitch. For example, U.S. Pat. No.7,632,239 (Dar) discloses foot sensor device for gait enhancementcomprising a sensor unit having an external casing, said sensor unitbeing positioned within a shoe of a user and sensing a parameterassociated with a gait event An electronic communication unit iselectrically associated with said sensor unit, for receiving a signalpertaining to said parameter The electronic unit has (i) amicrocontroller, (ii) a transmitting module for transmitting, in awireless fashion, gait information based on said signal, to a unit ofthe orthosis external to the foot sensor device, and (iii) a housing forhousing at least one of said microcontroller and said transmitting unit.A fastening unit is attached to said housing, said fastening modulebeing adapted to fasten on to said shoe, so as to secure said electroniccommunication module in a substantially fixed position during gait ofsaid user and including a clamp module for fastening onto a rim of theshoe. In the field of analysing weight shift to different parts of thefoot during golf or other sports U.S. Pat. No. 7,758,523 (Collings)discloses an orthotic body including an arch support, a cavity beingformed in that support and a wireless transmitter being built into thecavity.

SUMMARY OF THE INVENTION

A problem with which some embodiments of the invention is concerned ishow to fit a wireless footswitch including its battery into footwearunobtrusively while avoiding damage and early failure of components andproviding adequate working lifetime in a single battery which in somepatients is expected last at least three weeks between replacements. Afurther problem in embodiments of such devices is to provide low latency(e.g. about 20 milliseconds) on sending gait data e.g heel rise and heelstrike from quiescent stand-by states.

In one aspect the invention provides a shoe insole having a cavityopening to its lower face and a force or pressure sensor, sensor statemonitoring circuits, a wireless transceiver for transmitting sensorstate information and a battery for providing power, all located in saidcavity.

In another aspect the invention provides a shoe insole having a cavityconfigured to provide an internal pocket open to a face of said insole.The shape of the cavity may be arbitrary (e.g. it might in someembodiments be square or oval) but in preferred embodiments it hashaving a length greater than its width, a depth which is a smallfraction of its width and is directed generally along the length of theinsole, a segmented structure being slideably insertable into saidcavity within it is removably retained, the segments being disposedalong the cavity and housing a load or pressure sensor, sensor statemonitoring circuits, a wireless transceiver and a battery, adjacentsegments being electrically connected together and mechanicallyconnected together by links configured to maintain the spacing betweensegments while permitting flexion between adjacent segments under loadsencountered during walking.

In a third aspect the invention provides an electrical stimulator forattachment to the body comprising first and second electrodes forattachment to the body to apply an electrical stimulus, an insole as setout above, and a transceiver forming part of the simulator forcommunicating with the insole and providing the electrical stimulus inresponse to information received from the insole.

In a fourth aspect the invention provides a wireless footswitch modulefor fitting into a cavity formed along an insole of a shoe, saidfootswitch comprising a segmented structure having a length greater thanits width and a depth which is a small fraction of its width, thesegments housing a pressure sensor, sensor state monitoring circuits, awireless transmitter and a battery, adjacent segments being electricallyconnected together and mechanically connected together by linksconfigured to maintain the spacing between segments while permittingflexion between adjacent segments under loads encountered duringwalking. The elongated profile of the wireless footswitch and itssegmented construction enable the wireless footswitch module to fitwithin the outline of the insole with its edges well within the edges ofthe insole and allows the device to flex longitudinally and e.g. totwist slightly to conform to the shoe profile and to accommodatewalking. Advantageously the segment containing the wireless transceiverand other electrical components is located in the middle of the e.g.three segments to minimize loading.

In a fifth aspect the invention provides a footwear insole having acavity and a load, force or pressure sensor, sensor state monitoringcircuits, a wireless transceiver for transmitting sensor stateinformation and configured to join an ad hoc wireless network (e.g. aZigBee network), an accelerometer and a battery for providing power, alllocated in said cavity, the monitoring circuits being responsive toacceleration (e.g. shaking) and/or orientation detectable via theaccelerometer to change from a working mode to a network joining mode.In this way a user can initiate joining between the insole with thebuilt-in wireless footswitch module and a stimulation module withouthaving to access switches or other devices which may be inaccessiblebecause they are concealed within the insole. Close proximity bondinge.g. virtual contact between the modules to be joined may be necessarybefore joining can take place.

In a further aspect the invention provides a wireless insole for use inassociation with a removable wireless module, said insole having aninternal cavity configured for receiving the wireless footswitch module,said cavity extending longitudinally away from a heel region of theinsole and opening at an end facing away from the heel region. In someembodiments the cavity may be an elongate cavity.

In a further aspect the invention provides the use of apparatus asaforesaid in the treatment of dropped foot.

In a further aspect the invention provides a sensor module having awireless transceiver, a microcontroller and an accelerometer andconfigured to communicate with a second module via an ad-hoc wirelessnetwork and to switch from a sensing mode to a network joining mode onsensing via the accelerometer a predetermined movement or movements.

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the insole may be of ¾ length or full length and may beof thickness 4-10 mm. It may be a layered structure with the layersorientating themselves to form or mould to the profile of the shoe andfoot. Alternatively it may be a plastic or rubber material, e.g. asilicone elastomer, the Salford Insole providing an example of such anorthotic insole. It need not have an arch support, and can be anordinary insole having generally planar upper and lower surfaces, theinsole being only a few mm in thickness so that it can be fitted toordinary shoes or other footwear.

Embodiments of the insole have a cavity configured to provide aninternal pocket having an opening to one of its faces and mostconveniently its lower face into which the pressure sensor, sensor statemonitoring circuits, wireless transceiver and battery are slideablyinsertable and within which pocket they are removably retained. Thecavity in some embodiments has a length greater than its width and isdirected generally along the longitudinal direction of the insole, and acombined footswitch and transceiver of segmented structure is disposedin said cavity with its segments extending along the cavity and housingor holding the sensor, sensor state monitoring circuits, wirelesstransceiver and battery, adjacent segments being electrically connectedtogether and mechanically connected together as aforesaid. Embodimentsof the present insole have a cavity with an aspect ratio of about 2:1 toabout 4:1 e.g. about 3:1. The aspect ratio is a measure of overalllength to greatest width, excluding minor components e.g. a handle for abattery carrier. The cavity is closed sat its end facing towards theheel region of the insole and opens at its end facing away from theheel, as shown in the accompanying drawings.

In embodiments the combined sensor and transceiver comprises first,second and third segments disposed in a linear chain, the second segmentpositioned to underlie the arch of the foot holds the sensor statemonitoring circuits and transceiver, a first segment is positioned tounderlie the heel (more commonly) or ball of the foot and holds thesensor and third segment holds the battery the third segment lyingclosest to the opening of the pocket and being provided with a handle(not counted when considering aspect ratio) by which the segmentedstructure can be inserted into and removed from the cavity. The handlemay form part of a cell carrier that is slideably insertable endwiseinto and removable from the third segment.

In embodiments leads of the sensor extend from the first segment intothe second segment and are held in contact with conductive regions on acircuit board forming part of said second segment by an elastomericmember in compression, e.g. a block of silicone elastomer. Thisarrangement permits fast replacement of the sensor without the need tomake soldered connections to the circuit board in the segment whichcontains the active components. The battery may be a coin cell e.g. ofdiameter about 25 mm.

The segments in embodiments comprise plastics material e.g polyethylene,ethylene-propylene copolymer or polypropylene connected by strapconnectors behaving at least to some extent as living hinges. Theadjacent segments may be connected by integrally molded connectors eachserving as a living hinge. In embodiments the connection is by a pair oflaterally spaced connector bars, each connector bar providing linksconfigured to maintaining the spacing between segments while permittingflexion and rotation between the adjacent segments under loadsencountered during walking.

The sensor state monitoring circuits in embodiments include amicrocontroller having an ADC input configured to monitor the state ofthe sensor, the microcontroller having a power-saving mode in which amicroprocessor or core forming part of said microcontroller can bedisabled while inputs continue to be active. The wireless transceiverhas a stored identity for recognition by a stimulation module to whichit has been joined and forming a component of a a self-organizing ad-hocdigital network e.g. obeying a ZigBee protocol.

The network joining mode may involve close proximity of the wirelessfootswitch module and the stimulation module. A predetermined movementfor entry into the joining mode may comprise shaking or placing themodule in a predetermined orientation. A timer forming part of themodule may in some embodiments provide the joining mode to be operativefor a predetermined period, after which the module reverts to standardoperation.

The stimulation module may be configured for attachment to the humanbody or for attachment to or fitting to clothing.

BRIEF DESCRIPTION OF THE DRAWINGS

How the invention may be put into effect will now be described, by wayof example only, with reference to the accompanying drawings, in which:

FIG. 1 shows diagrammatically a known stimulation module according tothe invention with electrodes applied to the leg and a foot switch underthe user's heel;

FIG. 2 is a simplified block diagram of a stimulator module forming partof a functional electrical stimulator according to the invention;

FIG. 3 is a simplified block diagram of a footswitch module for use withthe stimulator module of FIG. 2;

FIG. 4 is a trimetric view from above of a segmented structure removablyinsertable into an insole pocket and incorporating sensor, activecomponent and battery segments mechanically connected together, somecomponents in the block diagram not being seen in the active componentsegment;

FIG. 5 is an exploded view of the segmented structure of FIG. 4;

FIG. 6 is a trimetric underneath view of a ¾ insole with a segmentedstructure partly removed from its pocket and with a battery and carrierremoved from the battery segment;

FIG. 7 is a trimetric underneath view of the insole of FIG. 6 with thesegmented structure in place in the pocket;

FIG. 8 is a flowchart showing how the footswitch module can be made totoggle between network joining mode and its normal sensing mode; and

FIG. 9 is a view of a full-length insole with a segmented footswitchmodule as aforesaid in place in a pocket.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Functional Electrical Stimulation

The present invention provides an improvement on known apparatusdisclosed in FIG. 1 which is an electronic device designed to assistpeople who have a dropped foot due to neurological damage that inhibitswalking. As previously explained, a dropped foot, the inability to lifta foot whilst walking, resulting in the foot being dragged forward orswung out to the side, is a common disability following neurologicalinjury. By stimulating the common peroneal nerve at its most superficialpoint, passing over the head of the fibula bone, it is possible throughexcitation of the withdrawal reflex to cause dorsiflexion with degreesof hip and knee flexion. If this is timed with walking using a footswitch worn in the shoe, walking can be significantly improved. Thestimulus gives rise to a sensation like “pins and needles” and thepatient soon becomes used to it. The apparatus can be made of size e.g.72×62×26 mm and of weight 112 g including e.g. a PP3 internal battery.It can therefore be small and light enough to be worn in the pocket oron a belt clip. Wires worn under the clothing carry the electricalstimulus to self-adhesive skin surface electrodes on the side of theleg. A small foot switch is placed in the shoe under the heel. Theapparatus can be used as an assistive aid or as a training device tostrengthen the muscles and achieve voluntary control. Additionally thedevice has a role in physiotherapy gait re-education, allowing isolatedcomponents of the gait cycle to be practiced under the supervision of atherapist. Dorsiflexion and eversion in the swing phase of walkingproduces reduced tripping and falls, reduced compensatory activity,reduced effort of walking and improved walking speed and a reduction inpatient anxiety and depression. The module is not restricted to thetreatment of dropped foot, however, and it may be useful in thetreatment of

-   -   gluteal or quadriceps muscles in walking    -   gluteal or quadriceps muscles for training weight transfer or        sit-to-stand    -   hamstrings for increased knee flexion or reduced knee        hyperextension    -   calf muscles for push-off at terminal stance    -   triceps and posterior deltoid for improved arm swing/reduced        associated reaction in gait.

One way in which the known apparatus can be applied to the user's leg isshown diagrammatically in FIG. 1. The peroneal nerve 10 passes justunder the head of the fibula and bifurcates to form deep and superficialbranches. An active electrode 14 may be placed over the common peronealnerve just below the head of the fibula, and an indifferent electrode 16is located about 5 cm below and slightly medially of the activeelectrode over the motor point of the anterior tibialis. This is astandard position to produce a flexion withdrawal response.

The positions of the active and indifferent electrodes 14, 16 may bereversed to change the polarity of the stimulation, and in thisarrangement in some cases eversion can be decreased while stillproducing dorsiflexion. The more negative electrode is more effective inproducing stimulation than the more positive electrode so that changingelectrode polarity controls the site of stimulation. Provision may bemade to dynamically vary the polarity across a stream of stimulationpulses such that dorsiflexion and foot inversion/eversion can becontrolled during each part of the gait cycle. Such reversal of polaritycan permit muscle pairs to be controlled using a single pair ofelectrodes e.g. to stimulate the deep and superficial branches of theperoneal nerve. The deep branch of the peroneal nerve stimulates a groupof muscles including the anterior tibealis which can producedorsiflexion of the ankle. The superficial branch of the peroneal nervecontrols the fibularis longus muscle (also known as peroneus longus)which when injured gives rise to inability to evert the foot and thefibularis brevis (peroneus brevis) muscles and thereby control footinversion/eversion. The ability to control two groups of muscles by asingle pair of electrodes is advantageous from the standpoint of patientcompliance because patients find multiple electrodes in the same regionof the body tedious to apply. Foot switch 18 and the electrodes 14, 16are connected to a control module or unit 10 that includes controls andcircuitry described below.

Output current in an embodiment may be adjustable between 10 and 100 mA,default 10 mA with a typical pulse width of 180 μS. The user mayincrease contraction strength by increasing the pulse width,compensating for day to day variations in muscle fatigue, electrodeposition and battery condition or changes in muscle tone.

Block Diagram of the Stimulation Module

A circuit for the stimulation module 12 is shown in simplified blockdiagram form in FIG. 2. The module is managed by a PIC microcontroller20 which has a stored program input by a programming header 21 andaspects of which can be adjusted by a therapist for an individualpatient. An 8-bit microcontroller suffices and may in an embodiment be amicrocontroller of the PIC18F4685 family available from MicrochipTechnology Inc. The programming header 21 permits in system programmingof firmware including, as previously explained, parameters later set bythe therapist using the user interface of the device.

For communication with the footswitch module the microcontroller 20communicates with transceiver 30 provided with on-board antenna 32. Thetransceiver works at 2.4 GHz, complies with IEEE 802.15.4s and acts as anode of a self-organizing ad-hoc digital network, in this case complyingwith ZigBee. An advantage of that specification is an ability to becomeactive from sleep mode in time of ≦20 milliseconds so that the networkcan be in sleep mode for much of the time, average power consumption canbe kept low and battery life can be maximized.

Signals from the microcontroller 20 pass through voltage converter 41,digital potentiometer 42, a network comprising current limiting resistor43 and capacitor 45, filters 40 and output stage 46 to electrodes 14,16. The output stage may also be controlled by the microcontroller vialines 44. In one embodiment the output stage comprises a push-pullconverter having an output transformer whose primary is controlled by apair of 2N7002 and IRF7317 FETs and whose secondary is connected acrossthe electrode socket. In another embodiment an output transformer has aprimary connected into an H-bridge of four FETs and a secondary forconnection to the electrodes. Current may pass through a first pair oftransistors on supply of signals to gate inputs, or may flow through asecond pair of transistor on application of signals to gate inputs. Thetransistors may be pulse width modulated to achieve a desired waveformand may be operated in a region where they exhibit analog-type gatevoltage-response behavior. Modulating pulses are applied to their gatesat frequencies which in some embodiments are in the range 200 KHz-10 MHze.g. 2 or 8 MHz. At these frequencies the internal capacities of thetransistors which are of the order of a few picofarads smooth the outputwaveform.

The stimulation module 12 has a number of sockets and controls for theuser. A combined stimulation level and on/off switch 26 enables thecontraction strength to be controlled by adjusting the stimulation pulsewidth from 10 to 400 μs. The switch 26 in an embodiment takes the formof a control knob which can be depressed and held down to turn thestimulation module on and can be rotated clockwise or counterclockwiseto increase or decrease the output level. An output test button 24enables electrode positions to be tested by the therapist and by theuser and can be used by the therapist when the stimulator is being usedduring exercising to practice components of gait. When testing thecondition of the footswitch is not monitored and so the loading on theswitch has no influence on the test. An output indicator LED 23 flickerswhen the module has been triggered. A pause switch 22 is provided thatwhen the module is in walk or exercise mode may be used to start andstop operation of the module when pressed puts the apparatus into sleepmode, which will conserve the battery when the user sits down. To returnthe module to its active state, the user need only press the pauseswitch 22 again. A bleep is heard, and then the apparatus again respondsto the foot switch. The module can only be turned off when its outputhas been paused, otherwise there is a risk of it being turned offaccidentally while in use. To turn the stimulation module off the switchis rotated to its minimum position and the button 22 is held down. Anadvantage of this feature is that when the module is turned off, thepulse width setting is reduced e.g. to 1%. The user must reset the levelto resume use of the module. It has been found in practice that usersturn the device up through the day as their muscles become tired andhaving to reset the stimulation level when the device is newly turned onmeans that they do not receive an unexpectedly high level of stimulationwhen they turn the device on the next day. The recommendation forpatients is that the module should therefore not be turned off using thecontrol knob through the day but put into sleep mode using the pauseswitch. When the module has been turned on and is paused, a setuproutine forming part of the program stored in microcontroller 20 can beaccessed. This may be e.g. by depressing and holding down the switch 26and within a predetermined period operating both the pause switch 22 andthe test button 24. Details of the setup routine are disclosed in WO2011/042736 the contents of which are incorporated herein by reference.In addition controls may be provided e.g. a sequence of operations forputting the module into joining mode where it receives a stored ID of afootswitch with which it is to communicate and a working mode, closephysical proximity optionally being required to enable joining to takeplace.

Block Diagram of the Footswitch Module

A footswitch module or unit is shown in FIG. 3 and is based on amicrocontroller 50, in this case a PIC LF14K22 which is an 8-bitmicrocontroller available from Microchip Technology Inc. and has astored program input via program header 58.

The microcontroller receives signals indicating phase of walking e.g.heel rise and heel strike from a pressure sensor 52 via an ADC input andis in serial communication with wireless transceiver 54 corresponding tothe transceiver 30 of the stimulation module, having an on-board antennaand complying with the ZigBee protocol. The pressure sensor ispreferably a force-sensitive resistor forming part of a voltage divideras disclosed in U.S. Pat. No. 6,507,757 or WO 2011/042736 (Lane), thedisclosure of which is incorporated herein by reference.

The microcontroller 50 is in serial communication with accelerometer 56which may be an ADXL 345 3-axis accelerometer which has FIFO technologyto minimize host processor load, provides activity/inactivitymonitoring, low power or standby modes to enable intelligentmotion-based power management and provides output data accessiblethrough an SPI digital interface. It serves two functions. It can beused as a mode switch providing a “shake to join” feature e.g. onshaking of the module by the user to switch the microcontroller 50 froma working mode to a bonding mode in which the stimulation module andfootswitch module share stored addresses and selective communicationbetween them through ZigBee is enabled. The shake function has theadvantage that the user can change mode of operation without having toremove the electronic module from the insole. Desirably each footswitchshould only communicate with the stimulation module for which it isintended, so that if there are two people in the same room there is nocross-talk between the footswitches and stimulation modules. Theaccelerometer 56 can in some embodiments detect user activity/inactivityand control entry of microcontroller 50 into its working and low powerstates. In further embodiments it may be used to detect heel rise andheel strike during walking A flowchart for an embodiment is shown inFIG. 8, from which it will be apparent that the footswitch module entersjoining mode for a predetermined time set by an internal timer which maybe a stored routine (a) on pressing the switch 60 described below, (b)on the accelerometer detecting shaking or (c) on the accelerometerdetecting movement of the module to a predetermined position (e.g. to anupright position). After the predetermined joining time has elapsed themodule is configured to revert to its normal sensing mode e.g. itspressure-sensing mode.

As previously mentioned the footswitch module also includes a pushbutton switch 60 which can be configured so that the module will enterjoining mode for a predetermined period e.g. one minute when power isturned on and then to enter its normal working mode. The push button canbe actuated through the casing via hole 93. The module also includes LED66 for indicating the state of the circuit, e.g. the LED flashing whenthe module is in bonding mode. Power is supplied by 3V lithium coin cell62 and reverse polarity protection MOSFET 64.

Segmented Footswitch Module and its Fitting to an Insole

For building a footswitch module having the components described aboveinto a shoe insole, regard has to be had to the pressure fields actingbetween the plantar surface of the foot and the insole and the movementof the insole during walking Pedobarography shows that the highestpressures during walking are exerted at the heel, in the middle of theball of the foot and at the big toe, and that pressure underneath thelongitudinal arch of the foot is relatively low. Pressures will changeand the sole of the user's shoe will flex during walking and it isdesirable that the footswitch module should be able to withstand theseforces and movements during use.

In FIGS. 4 and 5 a segmented footswitch and transmitter structurecomprises sensor segment 70, an active component segment 72 and abattery segment 74 with adjacent segments mechanically and electricallyconnected together, the mechanical connections maintaining the spacingbetween permitting the segments while permitting limited relativemovement between them under the forces encountered during walking. Wheninserted into the insole pocket the sensor segment 70 (which mostcommonly underlies the user's heel) is deepest into the pocket and thebattery segment 74 is closest to the opening of the pocket, the segments72 and 74 locating between the heel and ball of the foot where they arenot subject to the highest pressures during walking.

Sensor segment 70 comprises lower sheet 76 of polypropylene or otherplastics material having a generally circular body and lateral connectorstraps 80, 82 extending towards the active component segment 72 intowhich they locate by passing through end slots in cover 90 withthickened end regions 81, 83 having fixing holes 85, 87 locating ontodepending posts (not shown) on the concealed face of the cover 90. Eachstrap is stiff enough to maintain the segment spacing while permittinglimited relative movement between segments e.g. at or between positions80 a, 80 b. Pressure-sensor 52 is constructed as described in FIGS.13a-13e of U.S. Pat. No. 6,507,757 (Swain) the disclosure of which isincorporated herein by reference and has a circular body of diameterabout 25 mm and leads 84, 86 projecting towards and into the segment 72.A circular cover 78 of poron sheet fits onto and is adhered to lowersheet 76 with the footswitch 52 sandwiched between them and the leads84, 86 protruding.

In embodiments the pressure sensor is of width or diameter about 25 mmand has an open-circuit resistance of ≧100 KΩ with no load applied,falling below about 5 KΩ under load. In embodiments the pressure sensorcomprises a pressure-sensitive resistor having an active portioncomprising an array of fingers in contact with a conductive pad so thatmechanical pressure urging the pad towards the fingers reduces theresistance of the sensor. Such a pressure-sensitive resistor maycomprise a first insulating plastics sheet formed with a head region andrelatively narrow lead-defining extensions, conductive metal in apattern on the plastics sheet defining an inter-digitated arrayconnected to leads extending along said lead-defining extensions, asecond insulating plastics sheet having a head conforming to the headregion of the first insulating plastics sheet, and having stubprojections for covering proximal regions of the lead-definingextensions of the first plastics sheet, a layer of semiconductivematerial on the second insulating plastics sheet, the second insulatingplastics sheet having a surface with a texture or roughness or contentof conductive material such that when pressed against the electrodes ofthe array it forms an connection between the fingers of the opposedsides of the array, and an adhesive layer securing the first and secondplastics sheets together.

Active component segment 72 has a lower board 88 which is a PCB carryingthe microprocessor 50 (not shown in FIG. 5), transceiver 54, on-boardantenna 55, switch 60, reverse polarity protection 64 (not shown in FIG.5), LED 66 (not shown in FIG. 5) and accelerometer 56 (also not shown inFIG. 5). Power leads 97, 99 from the battery segment 94 connect to thePCB 88. Cover 90 is fixed to the lower sheet, concealing the PCB and thecomponents thereon save for transceiver 54 which appears through arectangular cut-out in the cover 90 in order to minimize the depthrequired for segment 72. Fixing of the cover 90 over the PCB is bycounter-sunk screws 93, 95 and nuts 92, 95 fitting into hexagonalrecesses in the cover 90. It will be appreciated that other fasteningarrangements are possible e.g. formations on the PCB 88 could snapengage with corresponding formations of cover 90.

Battery segment 74 is of polypropylene has upper and lower sheets 104,105 and walls on three sides defining a battery receptacle with springcontacts 110 visible in this view for making electrical contact withcoin cell 62 which in this instance is of diameter 24.5 mm. Leads 97, 99extend from the battery receptacle to the active component segment 72.Battery carrier 108 is a sliding fit into the battery receptacle and hashandle 109 which firstly enables battery insertion and removal andsecondly facilitates placement and removal of the segmented wirelessfootswitch module into and from the pocket in the insole. GenerallyC-shaped cover 106 fits around the battery receptacle covering the leads97, 99 at their ends extending into the segment 94 and is held in placeby fixing screws 115, 117 and by nuts 14, 115 which fit into hexagonalrecesses in the top face of cover 106. Again, other fitting mechanismse.g. a snap fit arrangement are possible. The covers 90, 106 are asingle injection molding in polypropylene or other flexible engineeringplastics and are connected by a pair of laterally spaced straps 100,102. Again the straps mechanically interconnect segments 72, 74 tomaintain spacing between them while permitting limited relative movementunder the forces encountered during walking. The aspect ratio of thesegmented wireless footswitch module (not including handle 109) is about3.

FIGS. 6 and 7 show the segmented wireless footswitch module fitted to apocket in the underside of ¾ length insole 120 of depth 4-5 mm which isformed in layers 122, pocket 124 opening to the lower face of the insoleand the upper face (not shown) being plain so that the module is whollyconcealed within the insole. Pillars (not shown) within the layers limitrelative sliding movement of the layers and may assist in prolonging theuseful life of the insole. The insole material may be mixed and notnecessarily produced from material of a single composition or physicalproperties. The layers may be soft or hard (different densities) asrequired to produce an insole that flexes to accommodate walking butalso enables effective actuation of the sensor segment 70. FIG. 8 is anunderneath view of a full length insole which for some users may reducein-shoe insole movement, a segmented footswitch module fitting into apocket as before in insole 130.

It will be appreciated that modifications may be made to the embodimentdescribed above without departing from the invention. For example if itwere desired to monitor both heel strike and toe-off an additionalfootswitch could be fitted to the module described above. Provision maybe made so that an OML footswitch can be attached to the middle PCB 88and trigger the wireless module as would the sensor 52. This requirementmay arise (a) if the clinician desires to trigger from the firstmetatarsal head and not the heel and (b) for those which the insolecannot fit in their footwear and the wireless footswitch module is wornoutside of the shoe. Although the ZigBee protocol is preferred, othernetworking protocols could be used or the two transceivers could simplybe made in matched pairs as is conventional in low power radioapplications. If monitoring of both feet is required, then an insolewith a wireless footswitch module could be provided for each foot, andboth could be proximity bonded to the same stimulation module.

The invention claimed is:
 1. A shoe insole for use in functionalelectrotherapy having a cavity opening to its lower face and a wirelessfootswitch module located in said cavity, wherein said footswitch modulecomprises: a load, force or pressure sensor; a microcontroller forreceiving signals from the sensor indicating phase of walking and havinga power-saving mode in which a microprocessor or core forming part ofsaid microcontroller can be disabled while inputs continue to be active;a wireless transceiver in communication with the microcontroller fortransmitting sensor state information; a battery for providing power;and an accelerometer for monitoring user activity/inactivity andcontrolling entry of the microcontroller into working and power-savingmodes; wherein the accelerometer is a 3-axis accelerometer having FIFOtechnology for minimising host processor load, has low power or standbymodes for intelligent motion-based power management and has an SPIdigital interface for providing output data.
 2. The shoe insole of claim1, wherein the wireless transceiver is configured to operate accordingto a ZigBee protocol.
 3. The shoe insole of claim 1, wherein the cavityis configured to provide a pocket within said insole having an openingto the lower face of the insole into which the wireless footswitchmodule is slideably insertable and within which pocket it is retaineduntil removed.
 4. The shoe insole of claim 3, wherein the cavity has alength greater than its width and is directed generally along thelongitudinal direction of the insole, and wherein the module is asegmented structure is disposed in said cavity with its segmentsextending along the cavity and holding the sensor, sensor statemonitoring circuits, wireless transceiver and battery, adjacent segmentsbeing electrically connected together and mechanically connectedtogether by links configured to maintain the spacing between segmentswhile permitting flexion between adjacent segments under loadsencountered during walking.
 5. The shoe insole of claim 4, wherein oneof said segments is positioned to underlie the arch of the foot andholds the sensor state monitoring circuits and transmitter, a secondsegment which holds the sensor is positioned to underlie the heel of thefoot or to underlie the ball of the foot and a third segment holds thebattery which is a coin cell.
 6. The shoe insole of claim 5, wherein thesensor is a pressure-sensitive resistor an open-circuit resistance of≧100 KΩ with no load applied, falling below about 5 KΩ under load, thesensor having an active portion comprising an array of fingers incontact with a conductive pad so that mechanical pressure urging the padtowards the fingers reduces the resistance of the sensor.
 7. The shoeinsole of claim 6, wherein the sensor comprises: a first insulatingplastics sheet formed with a head region and relatively narrowlead-defining extensions; conductive metal in a pattern on the plasticssheet defining an inter-digitated array connected to leads extendingalong said lead-defining extensions; a second insulating plastics sheethaving a head conforming to the head region of the first insulatingplastics sheet, and having stub projections for covering proximalregions of the lead-defining extensions of the first plastics sheet; alayer of semiconductive material on the second insulating plasticssheet, the second insulating plastics sheet having a surface with atexture or roughness or content of conductive material such that whenpressed against the electrodes of the array it forms an connectionbetween the fingers of the opposed sides of the array; and an adhesivelayer securing the first and second plastics sheets together.
 8. Theshoe insole of claim 7, wherein leads of the sensor extend from thesensor segment into the active component segment and are held in contactwith a circuit board forming part of said active component segment by anelastomeric member in compression.
 9. The shoe insole of claim 8,wherein the elastomeric member comprises a block of silicone elastomer.10. The shoe insole of claim 1, further comprising: first and secondelectrodes for attachment to a body to apply an electrical stimulus; anda transceiver communicating with the microcontroller and providing theelectrical stimulus via the first and second electrodes in response toinformation received from the transceiver.
 11. An electrical stimulatorfor attachment to a body, comprising: first and second electrodes forattachment to the body to apply an electrical stimulus; a shoe insolefor use in functional electrotherapy having a cavity opening to itslower face and a wireless footswitch module located in said cavity,wherein said footswitch module comprises a load, force or pressuresensor, a microcontroller for receiving signals from the sensorindicating phase of walking and having a power-saving mode in which amicroprocessor or core forming part of said microcontroller can bedisabled while inputs continue to be active, a wireless transceiver incommunication with the microcontroller for transmitting sensor stateinformation, a battery for providing power and an accelerometer formonitoring user activity/inactivity and controlling entry of themicrocontroller into working and power-saving modes; and a transceiverforming part of the simulator for communicating with the insole andproviding the electrical stimulus via the first and second electrodes inresponse to information received from the insole; wherein theaccelerometer is a 3-axis accelerometer having FIFO technology forminimizing host processor load, has low power or standby modes forintelligent motion-based power management and has an SPI digitalinterface for providing output data.
 12. The electrical stimulator ofclaim 11, wherein: the cavity is configured to provide a pocket withinsaid insole having an opening to the lower face of the insole into whichthe wireless footswitch module is slideably insertable and within whichpocket it is retained until removed.
 13. The electrical stimulator ofclaim 12, wherein: the cavity has a length greater than its width and isdirected generally along the longitudinal direction of the insole, andwherein the module is a segmented structure is disposed in said cavitywith its segments extending along the cavity and holding the sensor,sensor state monitoring circuits, wireless transceiver and battery,adjacent segments being electrically connected together and mechanicallyconnected together by links configured to maintain the spacing betweensegments while permitting flexion between adjacent segments under loadsencountered during walking; and one of said segments is positioned tounderlie the arch of the foot and holds the sensor state monitoringcircuits and transmitter, a second segment which holds the sensor ispositioned to underlie the heel of the foot or to underlie the ball ofthe foot and a third segment holds the battery which is a coin cell. 14.The electrical stimulator of claim 11, wherein the sensor is apressure-sensitive resistor an open-circuit resistance of ≧100 KΩ withno load applied, falling below about 5 KΩ under load, the sensor havingan active portion comprising an array of fingers in contact with aconductive pad so that mechanical pressure urging the pad towards thefingers reduces the resistance of the sensor.
 15. The electricalstimulator of claim 11, wherein the sensor comprises: a first insulatingplastics sheet formed with a head region and relatively narrowlead-defining extensions; conductive metal in a pattern on the plasticssheet defining an inter-digitated array connected to leads extendingalong said lead-defining extensions; a second insulating plastics sheethaving a head conforming to the head region of the first insulatingplastics sheet, and having stub projections for covering proximalregions of the lead-defining extensions of the first plastics sheet; alayer of semiconductive material on the second insulating plasticssheet, the second insulating plastics sheet having a surface with atexture or roughness or content of conductive material such that whenpressed against the electrodes of the array it forms an connectionbetween the fingers of the opposed sides of the array; and an adhesivelayer securing the first and second plastics sheets together, whereinleads of the sensor extend from the sensor segment into the activecomponent segment and are held in contact with a circuit board formingpart of said active component segment by a block of silicone elastomeror other elastomeric member in compression.
 16. A wireless footswitchfor use in functional electrotherapy comprising in combination: aremovable shoe insole comprising a single cavity configured to providean internal pocket open to a face of said insole at an opening, thecavity having a length greater than its width and being directedgenerally along the length of the insole; and a single segmentedstructure having a length greater than its width and configured forslidable insertion through said opening in said face of said soleendwise into said cavity, said structure being inserted into said cavitywithin which it is removably retained; the segments being disposed alongthe cavity and housing a pressure sensor, sensor state monitoringcircuits, a wireless transmitter and a coin cell battery; adjacentsegments being electrically connected together and being mechanicallyconnected together by flexible hinge links configured to maintain thespacing between segments while permitting flexion between adjacentsegments under loads encountered during walking; and the singlesegmented structure having first, second and third segments disposed ina linear chain wherein a first segment houses the pressure sensor, asecond segment located in a middle of said first, second and thirdsegments houses the sensor state monitoring circuits and wirelesstransmitter and a third segment holds the coin cell battery.
 17. Thewireless footswitch of claim 16, wherein the sensor is apressure-sensitive resistor having an array of fingers in contact with aconductive pad so that mechanical pressure urging the pad towards thefingers reduces the resistance of the sensor and comprising: a firstinsulating plastics sheet formed with a head region and relativelynarrow lead-defining extensions; conductive metal in a pattern on theplastics sheet defining an inter-digitated array connected to leadsextending along said lead-defining extensions; a second insulatingplastics sheet having a head conforming to the head region of the firstinsulating plastics sheet, and having stub projections for coveringproximal regions of the lead-defining extensions of the first plasticssheet; a layer of semiconductive material on the second insulatingplastics sheet, the second insulating plastics sheet having a surfacewith a texture or roughness or content of conductive material such thatwhen pressed against the electrodes of the array it forms an connectionbetween the fingers of the opposed sides of the array; and an adhesivelayer securing the first and second plastics sheets together, leads ofthe sensor extending from the sensor segment into the active componentsegment and being held in contact with a circuit board forming part ofsaid active component segment by a block of silicone elastomer or otherelastomeric member in compression.
 18. A wireless footswitch for use infunctional electrotherapy comprising in combination: a removable shoeinsole comprising a single cavity configured to provide an internalpocket open to a face of said insole at an opening, the cavity having alength greater than its width and being directed generally along thelength of the insole; and a single segmented structure having a lengthgreater than its width and configured for slideable insertion throughsaid opening in said face of said sole endwise into said cavity; thesegments being disposed along the cavity and housing a pressure sensor,sensor state monitoring circuits, a wireless transmitter, and a coincell battery; adjacent segments being electrically connected togetherand being mechanically connected together by links configured tomaintain the spacing between segments while permitting flexion betweenadjacent segments under loads encountered during walking, said linksbeing either strap connectors behaving as living hinges or a pair oflaterally spaced connector bars, each connector bar providing linksmaintaining the spacing between segments while permitting flexion androtation between the adjacent segments under loads encountered duringwaking; and the segmented structure having first, second and thirdsegments disposed in a linear chain wherein a first segment houses thepressure sensor, a second segment located in a middle of said first,second and third segments houses the sensor state monitoring circuitsand wireless transmitter and a third segment holds the coin cellbattery.